. >>> fbi investigators were expected to arrive today at the u.s. consulate in benghazi, libya, where attackers killed a u.s. ambassador and three other americans. but they postponed the trip until the volatile region is safer. senior international correspondent arwa damon went inside the battered compound and shows us firsthand how the attack occurred. >> amid the ash, soot and debris, remnants of a life that was. and what it meant to those stationed here. scrawled on this sheet, libya is so important. traces of bloodstained the walls. what's now a blackened ruin was a pleasant compound in an upscale benghazi neighborhood. libyan officials say tuesday night's attack was planned by islamist militants. and quickly overwhelmed the libyan and american guards. the compounds' first line of defense, easily breached. according to one of the libyan guards stationed at the gate, armed with only a radio the assault happened simultaneously from lee different directions. and he says that he initially heard chanting growing increasingly louder and then suddenly